"Fog" lights vs Aux/Driving lights

I would usually not bother to comment or post about stuff like this but I feel that I'm not doing anyone any favors if I keep this to myself. First a little background. I worked for many automotive electronic installation companies over the years and also had a successful automotive electronics and diagnostics business for even longer and had noticed a lot of confusion about this topic that I rarely see debugged.

A VERY COMMON misconception for at least 40 years is what a fog light is and how it's suppose to work. Part of this isn't actually the fault of owners of vehicles with "fog lights" but because the OEM/Manufacturers often mislabel these lights on the dashboard and this has caused a lot of confusion over the many decades. It all started back in the early 80s if I recall when OEM "fog lights" were installed on many different model vehicles.

Two issues that caused this misconception. The first was that the lights on the dash were actually Labeled "Fog" lights and often showed a light beam with a wavy line...so, this tells everybody these are meant for driving in fog. Of course, right?! Not necessarily.

The second issue that contributed to this misconception was the fact that the fog lights in many OEM applications would be allowed to work WITH the headlights. Lets clarify two VERY important things about fog lights. First real "Fog" lights (that actually work in fog) have a very wide but super narrow beam...not a round beam like headlights. So if the "Fog lights" in your vehicle have a round type of beam, similar to headlights these are NOT fog lights but auxiliary driving lights. These type of lights, regardless of how they are labeled are to simply add additional lighting to your headlights and not for fog use.

So, fog lights can NOT be used effectively in actual fog with the headlights on! The headlight must be turned OFF in order for fog lights to effectively function. The reason why they are so different in functionality to a headlights or aux/driving lights is because the beam is so thin (top to bottom) there is simply not enough of light, height-wise to reflect back.

Did you ever notice in fog, if you were to flip your high beams on, how much worse it is to see with the light glare bouncing back at you as it reflects off the fog? THIS is why real/actual fog lights have the beam pattern that they have.

So to summarize. If the OEM fog lights in a vehicle can't be turned on independently from the headlights, even if the beam of that "fog light" is wide and thin, these lights are going to be ineffective if the headlights are on. This can be altered if you know what you're doing by changing the wiring a bit to allow the fog lights to be powered up while the headlights are off but with your parking/marker lights still on. But if the beam pattern of the "fog lights" isn't wide and thin, then they are not fog lights at all but auxiliary lighting designed to be used WITH your headlight for additional lighting.

If you do have real fog lights on a vehicle and have the chance to drive in really bad fog, real fog lights will actually make it like you're not driving in fog at all. It really does make this much of a difference BUT your headlights can't be on - otherwise they will wash out the fog light beam and the headlights will reflect back into the driver's eyes.

Oh almost forgot.
The color of a true fog light doesn't matter. Amber, yellow or clear. If the fog light has that wide, thin beam they will cut through the fog regardless. Oh a side note on color though. Since this "fog light" subject is so misunderstood....law enforcement are usually also just as confused and in some areas they may pull you over for not having your headlights on!! So it might be better to go with a clear fog light lens rather than amber or yellow just to make it look more to the unaware officer, that these are "headlight equivalents" as amber or yellow lenses will certainly draw more attention to your vehicle than clear lenses. I assure you if you have real fog lights on a vehicle, when driving in thick "pea soup" fog and you turn your headlights OFF with the fog lights on, you won't believe how affective they are!

MORE INFORMATION: When purchasing aftermarket lighting, purchase them with the thoughts of what I wrote above. If you want true fog lights, make sure you actually buy real fog lights. Honestly I think aux/driving AND fog lights are helpful.

It's highly recommended that when adding any type of AUX lighting (Fog or otherwise) - make sure the parking light are on, otherwise you won't have any rear or marker lights. This really should be wired so it happens automatically so you or any other driver doesn't forget to turn the parking lights on which would be dangerous at night driving around with out any parking/rear/marker lights.

The best way to do this is use a Single Pole/Single Throw (SPST) automotive relay. Use the parking light circuit to "trigger" the coil of the relay. On some vehicles the parking lights are switched negatively but on others the parking light are switched positively. So if the parking light switch is using positive voltage to turn the parking lights on, then you would ground pin #86 on the relay and pin #85 would be wired to the parking light circuit...if the parking light circuit is switched with negative, then pin #86 would go to a constant (un-switched) 12volt source and pin #85 would be wired to the parking light switch.

The new/aftermarket lights would be wired to pin #30 of the relay and pin #87 to a positive voltage source (rated high enough to power up the lights) WITH A FUSE in line. The fuse amperage should be about 10 percent higher than the amperage consumed by the lights. This is more just protection for a short circuit but would also protect against excessive current draw...although there is very little chance of this.

Another way to wire up fog lights only is to use a Single Pole, Double Pole (SPDP) relay to automatically shut off the OEM headlights when the fog lights are on. This will ensure that the driver doesn't have the headlights on in fog when the fog lights are on.

By the way - the reason for the relay as compared to wiring the aftermarket light directly to the OEM switch is two fold. 1) It doesn't place the OEM circuit under any more load because the aftermarket lighting is drawing it's power, not from the OEM switch but from an alternate 12volt source. 2) the relay completely isolates the new lights from the OEM lighting system which is very helpful, especially for LED lights that require some type of resistor (either external or built into the LED fixture). Remember that incandescent lights have a significant amount of resistance, LED do not. Thermal flashers used for hazard and directionals need this resistance in order to work correctly. The alternative is the newer electronic flashers which don't rely on the resistance of the incandescent bulbs but on a 555 timing IC chip inside the flasher unit.

 

Thanx for the write up.

 

You are very welcome. I'm not trying to be a "enlighten-er" or know-it-all but with all of the stuff going on with vehicle on forums like this I think it would really help some of these guys to understand the difference between the two and how they are suppose to work. There is no doubt that guys rebuilding or adding and improving equipment on their vehicle should know this.

 

i wont lie, i use em all the time cuz i think it looks cool.

 

Excellent write-up, thank you.
Though, I would say something about turning the headlights off when fogs are on in a real fog situation, this might not work if you are actually trying to drive through a fog in the dark.
Granted, the fog might not be that dense in the cities, but sometimes it can get pretty bad and I agree the headlight white kinda "bounce" off the fog, but the amber fog lights I have will cut through like a knife in soft butter.
In another thought, your thoughts on "real fog light" is more so OEM settings rather than light manufacturing declaration? I believe most newer Toyotas can turn on headlight/fogs only/DRL separately, but would that qualify as what you stated, "real fog lights?

 

First quick glance I thought it was a DMC....lol

 

91 Z28

 

YES! Very good point! This confusion for sure is more of an OEM side of things not aftermarket lights. If you purchase a product that is labeled "Fog Lights" they SHOULD be the real thing for sure. Ford and GM have mislabeled their lights in the 80s, 90s and I'm sure later on that really made the words "Fog Lights" this universal buzz word for any lighting that isn't the headlights. Weird how that happened. Of course testing out these lights is very straight forward....pull up to a flat wall or garage door at night, turn on the fog-lights and turn off your headlights. If the beam is thin and wide it's a real fog light, otherwise it's an aux/driving light.

 

Oh yeah...I agree. Using real fog light with the headlight is only going to add to the lighting (and look) but when it's actually foggy the headlight should be switched off for the fog lights to do their job. But without fog, hell turn everything on!!

 

LOL WTF?!! Holy crap that's insane!
Photoshop/GIMP modified or real??

 

What have y'all found to be the best 9006 LED bulb to use?